Projection display apparatus

ABSTRACT

A projection display device capable of improving cooling efficiency of the power unit includes a light source lamp unit, a projection lens unit, an exhaust fan provided near the light source lamp unit for ventilating an outer case, and a ventilating path provided inside the power unit. A suction fan is provided at the inlet of the ventilating path which is connected to the cooling air intake port through a duct cover to directly conduct fresh air into the ventilating path. Because the interior of the power unit is cooled by fresh air which is cooler than the air inside the outer case, cooling efficiency is enhanced.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a projection display apparatus which separateslight beams from a light source into red, blue and green light beams.The display apparatus modulates the red, blue and green light beamsthrough light valves provided in a liquid crystal panel in response toimage information. The modulated red, blue and green light beams arecombined and expansively projected through a projection lens on aprojection screen. In particular, the invention relates to a coolingsystem for efficiently and cleanly cooling the components of aprojection display device that separates, modulates combines andprojects light beams.

2. Description of Related Art

Conventional projection display devices include an optical unit whichoptically treats light beams emitted from a light source lamp unit tosynthesize a color image in response to image information. Thesynthesized light beams are projected on a screen through the use of aprojection lens unit, a power unit, and a circuit board unit includingcontrol circuits and similar devices.

The optical unit separates light beams emitted from the light sourcelamp unit into red, blue and green color light beams. The optical unitmodulates these color light beams with light valves provided in a liquidcrystal panel in response to image information. The modulated colorlight beams are recombined with a cross dichroic prism or similardevices, and are projected on a screen.

Japanese Patent Publication No. 7-225379 discloses a projection displayapparatus provided with a polarized light conversion device for aligningthe polarization direction of light beams emitted from a light sourcelamp unit. The polarized light conversion device has a polarized beamsplitter array provided with a plurality of sets of polarized lightseparating films and reflection films which are parallel to each other.The polarized beam splitter array separates incident light beams intotwo types of straight polarized light components, and aligns thepolarization direction of these two types of straight polarized lightcomponents.

Some elements of the projection display apparatus, e.g. the polarizedlight conversion device and the optical unit, are stored in an outercase. A projection side of the projection lens unit is disposed in theouter case such that it protrudes from the front face of the outer case.The outer case is provided with an operating section including a powerswitch, a light-receiving window for remote control, and an input/outputterminal group for sending and receiving signals to and from externaldevices.

Conventional projection display devices include optical devices in thelight source lamp unit, a power unit and an optical unit, all of whichare sources of heat. The liquid crystal light valves and theirrespective polarization plates are major heat sources because theyabsorb part of the transmitted light beams.

In order to cool the heat sources, the projection display apparatus isprovided with a cooling system.

The cooling system introduces fresh air into the outer case through anintake port by a suction fan. The introduced air is circulated throughthe outer case and exhausted through an air outlet provided on the outercase by an exhaust fan.

In such a cooling system, the power unit, which often become very hot,is provided with a suction fan to introduce the air in the outer case tothe interior of the power unit for cooling.

The power unit includes a primary active filter, a power supply, and aballast. A transmitter FET may be mounted on the circuit board of theprimary active filter. A rectifier diode bridge, an oscillatingtransistor for a D/D converter and a triode regulator for a D/Dconverter may be mounted on the circuit board of the power supply. Also,devices such as a driving FET for a chopper circuit and areverse-current preventing diode for a chopper circuit may be mounted onthe circuit board of the ballast. Because these devices are heatsources, heat sinks are fixed to them to enhance cooling efficiency. Airintroduced with the suction fan cools the heat sinks.

By the time that air is introduced to the power unit in the outer case,it has already been heated by many other elements located in the outercase. Thus, the air introduced to the power unit is hotter than thefresh air introduced into the outer case, and is less efficient incooling the power unit.

Also, when the air in the outer case is drawn with the suction fan,fresh air containing dust may be introduced through openings of theouter case, e.g., the gap between the projection lens unit and the outercase. As a result, dust may adhere to the optical system and deterioratethe display quality, which reduces the reliability of the apparatus.

The polarized light conversion device is heated because the polarizedlight separating film and the reflection film absorb some of theincident light. The device has no separate cooling means even though itmust be cooled. The polarized light conversion device is thereforecooled by the air circulating from the suction fan to the outlet. Thus,the device may not be efficiently cooled due to insufficient circulationof the cooling air in some apparatus configurations.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a projectiondisplay apparatus that includes a cooling system that efficiently coolsthe power unit and polarized light conversion device while preventingairborne debris from contaminating the apparatus.

In accordance with a first embodiment of the invention, a projectiondisplay apparatus includes an optical unit for forming an optical imagein response to image information by optically treating light beamsemitted from a light source lamp unit and for expansively projecting theoptical image on a projection area through a projection lens. Theprojection display device includes a power unit with a ventilating pathprovided inside the power unit for circulating cooling air. An outercase stores the optical unit and the power unit. The projection displayapparatus further includes a cooling air intake port formed on the outercase and a cooling air conducting means for directly conducting freshair from outside the outer case from the cooling air intake port to theinlet of the ventilating path.

Because the cooling air conducting means directly conducts fresh air tothe ventilating path, and because fresh air is cooler than the air inthe outer case, the interior of the power unit can be cooled with highefficiency.

A ventilating fan for ventilating the interior of the outer case ispreferably provided near the light source lamp unit. The air in theouter case, including the air exhausted from the ventilating path, iscollected near the light source lamp unit before being exhausted to theexterior. Thus, the heated light source lamp unit can be securelycooled.

It is preferred that the cooling air conducting means include a ductsection connecting the cooling air intake port and the inlet of theventilating path. Accordingly, the duct section only introduces freshair from the cooling air intake port to the ventilating path. The ductsection also prevents the air from the outer case, which is hotter thanthe fresh air, from entering into the ventilating path. The interior ofthe power unit can therefore be more efficiently cooled.

The cooling air conducting means may also include a suction fan providedat the inlet of the ventilating path for drawing fresh air into theventilating path. A large volume of fresh air can therefore be stablysupplied to the ventilating path, and the power unit can be securelycooled with high efficiency.

The duct section securely prevents the suction fan from drawing dustinto the outer case through openings in the outer case such as the gapbetween the projection lens unit and the outer case. Dust can thereforebe prevented from adhering onto the optical system, which provides highimage display quality and satisfactory reliability.

Although the power unit provided with the suction fan does not have tobe located inside the outer case, the optical path from the light sourcelamp unit to the projection lens unit must be provided within the narrowspace in the outer case of the projection display apparatus. The powerunit is preferably arranged so that the suction fan is located in thefree space in the outer case in order to effectively use the space inthe outer case.

The projection lens may be provided so as to have an edge protrude fromthe outer case. The suction fan may be located on the base end of theprojection lens unit, and the cooling air intake port may be formed in aregion of the bottom wall of the outer case which includes the lowerside of the projection lens unit.

In the optical unit, the projection lens unit may protrude from thelight source lamp unit and the optical devices so that the combinedlight from the optical device is incident on the base end of theprojection lens. When the projection lens unit is arranged so as to havea front end protrude from the outer case, a dead space is formed at theside of the base end of the projection lens.

Because the power unit has a suction fan located on the base end of theprojection lens unit, the apparatus can be miniaturized as a result ofthe effective use of space in the outer case.

Further, because the cooling air intake port is formed in a region ofthe lower side of the projection lens unit, the duct section can beprovided in the dead space running from the lower side of the projectionlens unit to the side of its base end. Accordingly, space in the outercase is effectively used.

In accordance with another aspect of the invention, a projection displayapparatus includes an optical unit including a light source lamp unitand a projection lens unit for forming an optical image in response toimage information. The apparatus optically treats light beams emittedfrom the light source lamp unit and expansively projects the opticalimage on a projection screen through the projection lens unit. An outercase for storing the optical unit and a power unit includes aventilating fan for ventilating the interior of the outer case near thelight source lamp unit. The projection display apparatus furtherincludes a polarized light conversion device facing an emitting surfaceof the light source lamp unit for separating the light beams emittedfrom the light source lamp unit into two types of straight polarizedlight components and for aligning the polarizing direction of thestraight polarized light components. A ventilating path is providedinside the outer case for circulating cooling air along at least oneface among a light incident face and a light emerging face of thepolarized light conversion device.

Because the ventilating path circulates the cooling air along at leastone face among the light incident face and the light emerging face ofthe polarized light conversion device, the cooling air can securelycirculate near the polarized light conversion device to achievesatisfactory cooling effects regardless of the configuration of theapparatus.

A guide is preferably provided for introducing the cooling aircirculated along at least one face among the light incident face andlight emerging face of the polarized light conversion device to thelight source lamp unit.

In such an apparatus, the guide introduces the cooling air after coolingthe polarized light conversion device to the light source lamp unit toeffectively cool the light source lamp unit. The lamp life is thereforeprolonged, and replacement of the lamp is required less frequently.

The outer case may be provided with an operating section having aplurality of switches including a main on/off switch for main power. Aprotruding section may protrude from the main switch between the mainswitch and the switch adjacent to the main switch. Such a structureprevents erroneous operation of the main switch.

The protruding section is preferably provided along the periphery of themain switch. This structure also prevents careless contact with the mainswitch and thus securely prevents erroneous operation of the switch.

A circuit board may be provided on the optical unit. Atemperature-sensing element may be connected to the circuit board andlocated near the light source lamp unit to monitor the temperature ofthe lamp.

Such a structure effectively monitors the temperature of the lightsource lamp unit while obviating wiring between the temperature-sensingelement and the circuit board because the temperature-sensing element isdirectly mounted on the circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and advantages of the invention will becomeapparent from the following detailed description of preferredembodiments when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1(A) is a front view and FIG. 1(B) is a rear elevational view of aprojection display apparatus in accordance with a preferred embodimentof the invention;

FIG. 2(A) is a top view and FIG. 2(B) is a bottom view of the projectiondisplay apparatus in accordance with the preferred embodiment of theinvention;

FIG. 3 is an exploded perspective view showing the optical system andthe power unit in accordance with the preferred embodiment of theinvention;

FIG. 4 is a schematic representation of the optical system in accordancewith the preferred embodiment of the invention;

FIG. 5(A) is a cross-sectional view and FIG. 5(B) is an isometric viewof the polarized light conversion device in accordance with thepreferred embodiment of the invention;

FIG. 6 is a planar cross-sectional view showing the stream of coolingair in the projection display apparatus in accordance with the preferredembodiment of the invention;

FIG. 7 is a cross-sectional view showing the stream of cooling air inthe projection display apparatus in accordance with the preferredembodiment of the invention; and

FIG. 8 is a cross-sectional view showing the stream of cooling air inthe projection display apparatus in accordance with the preferredembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

While the invention will hereinafter be described in connection withpreferred embodiments thereof, it will be understood that it is notintended to limit the invention to those embodiments. On the contrary,it is intended to cover all alternatives, modifications and equivalentsthat may be included within the spirit and scope of the invention asdefined by the appended claims.

For a general understanding of the features of the invention, referenceis made to the drawings. In the drawings, like reference numerals havebeen used throughout to designate identical elements.

FIGS. 1(A) and 1(B) are a front view and a rear elevation view,respectively, of a projection display apparatus in accordance with apreferred embodiment of the invention. FIGS. 2(A) and 2(B) are a planview and a bottom view, respectively, of the projection displayapparatus in accordance with the preferred embodiment of the invention.

As shown in FIGS. 1(A)-2(B), the projection display apparatus 1 inaccordance with the preferred embodiment has a rectangularparallelepiped outer case 2. The outer case 2 may include an upper case3 and a lower case 4. The rear wall of the outer case 2 is provided withan AC inlet 36 for supplying external power to the apparatus and aninput/output terminal group 50. The apparatus is user-friendly becauseno signal cables or similar devices are placed on the side at whichusers generally stand.

The upper case 3 of the outer case 2 includes a rectangular top wall 3a,left and right side walls 3b and 3c, a front wall 3d and a rear wall 3e.The front wall 3d and rear wall 3e extend vertically from the four sidesof the upper wall toward the lower side. The lower case 4 includes arectangular bottom wall 4a, left and right side walls 4b and 4c, a frontwall 4d and a rear wall 4e. The front wall 4d and rear wall 4evertically extend from the four sides of the bottom wall.

The front wall 3d and the front wall 4d are dented on slightly leftportion of the center as shown in FIG. 2. The front end of a projectionlens unit 6 extends toward the front side of the apparatus from acircular opening formed thereon, and the top of the projection lens unitprotrudes from the front face of the outer case 2.

A zoom ring 61 holding a zoom lens in the protruding section of theouter case 2 has a protuberance 610, such as a linear knob, extending tothe axis line direction. The zoom ring 61 and a focus ring 62 cantherefore be tactily distinguished from each other and easily rotated.The protuberance 610 may be provided on the focus ring 62 as long as itdoes not prevent motion of the focus ring 62.

As shown in FIG. 1(A), a light-receiving window 35 is provided on thefront wall 3d of the upper case 3 on the right of the projection lensunit 6. The receiving window 35 is provided for receiving control lightbeams passing through a remote controller not shown in the drawings.

As shown in FIG. 2(A), a number of holes 25 are formed in the center ofthe front side of the top wall 3a of the upper case 3. A self-containedspeaker (not shown in the drawings) may be located behind the top wall3a.

The center of the front side of the top wall 3a is also provided with anoperating switch section 26. A main switch 261 for turning on/off themain power includes a protuberance section 262 provided between the mainswitch 261 and the adjacent switch 263 among switches formed on theoperating switch section 26. The protuberance section 262 protrudes fromthe main switch 261 and has an arc shape along the periphery of thecircular main switch 261. The protuberance is preferably located alongthe periphery of the main switch 261 along a 90 degree arc. Because thearc protuberance 262 protrudes from the top of the main switch 261,other switches can be operated without erroneously touching the mainswitch 261. Erroneous operation of the main switch can therefore besecurely prevented.

A foot 31C is provided in the center of the rear end of the bottom wall4a of the lower case 4, and feet 31R and 31L are provided on the leftand right sides of the front end. The height of the left and right feet31R and 31L, as measured from the bottom wall 4a, is adjustable byturning the feet.

FIG. 3 shows an arrangement of individual components inside the outercase 2 of the projection display apparatus 1. The outer case 2 isprovided with an optical unit 10 including the above-mentionedprojection lens unit 6 and a power unit 7 adjacent to each othertherein. A control board 13 for controlling the apparatus and a videoboard 11 are stacked on the optical unit 10.

The optical unit 10 includes a light source lamp unit 8 that includes alight source lamp 81 (shown in FIG. 4) stored in a housing 802. Anoptical lens unit 9 optically treats the light beams emitted from thelight source lamp unit 8 and forms an optical image in response to imageinformation. A projection lens unit 6 expansively projects the opticalimage onto a projection screen. The optical unit 10 occupies at leastthe right half of the internal space of the outer case 2.

The optical lens unit 9 includes a prism unit 910 and upper and lowerlight guides 901 and 902 containing various optical devices as describedbelow. The upper and lower light guides 901 and 902 are fixed to theupper case 3 and the lower case 4 shown in FIGS. 1(A) and 2(B),respectively, with fixing screws.

A rectangular cutout 9001 in the plan view shown in FIG. 3 is formed inthe center on the front side of the light guides 901 and 902 tofacilitate assembly of the prism unit 910.

The prism unit 910 is attached to a thick die-cast head plate 903 formedof magnesium or aluminum, and is fixed to the light guides 901 and 902via the head plate 903.

The head plate 903 is L-shaped which includes a vertical wall 91 alongthe width direction of the apparatus and a bottom wall 92 (shown in FIG.7) horizontally extending from the bottom of the vertical wall 91. Theprism unit 910 is fixed on the bottom wall 92. In the center of thevertical wall 91, a rectangular opening (not shown) is provided as apassageway for the light emerging from the prism unit 910. The base endof the projection lens unit 9 is fixed to the rectangular opening. Theprism unit 910 and the projection lens unit 6 are fixed to the opticallens unit 9 so as to sandwich the stiff vertical wall 91 therebetweenafter the optical system is aligned. These units are therefore formedintegrally, and misalignment of the optical system due to strong impactwill rarely occur.

The base end of the projection lens unit 6 is located in the center ofthe front side of the optical lens unit 9, and a gap in response to theprotruded length of the projection lens unit 6 from the outer case 2 isformed on the side of the base end, i.e., between the head plate 903 andthe front walls 3d and 4d of the outer case 2.

The corner portion of the rear section of optical lens unit 9 at theside of the power unit 7 includes an indent, and the light source lampunit 8 is assembled in the indent. That is, the light source lamp unit 8is provided at a rectangular area formed by the rear end of the powerunit 7 and the indent in the optical lens unit 9.

A lamp-replacement cover 27 is fixed with a screw to the bottom of wall4a of the lower case 4. A lamp can be replaced by loosening the screwand removing the cover 27 to expose the light source lamp unit.

A control board 13 for controlling the apparatus is fixed with screws onthe upper face of the optical lens unit 9. A video board 11 including avideo signal treating circuit is provided on the control board 13.

Because the control board 13 is fixed to the upper face of the opticalunit 10 with screws, the control board 13 and the optical unit 10 can betested using external power even when the whole assembly is notcompleted, such as in OEM production in which the control board 13 andthe optical unit 10 are fixed. The control board 13 has a cutout section130 at a location corresponding to, and overlapping with, the prism unit910. The boards 11 and 13 are electrically connected to each otherthrough connectors 114 and 116.

The power unit 7 is disposed on the left side of the optical unit 10 inthe left side of the outer case 2 in the rear view of the displayapparatus 1 as shown in FIG. 3.

The power unit 7 has an L shape to match the shape of the space betweenthe outer case 2 and the optical unit 10. The power unit includes a mainbody 71 located from the rear to the front of the apparatus and includesan extension 72 bending from the front end of the main body 71. Theextension 72 is located at the side of the base end of the projectionlens unit 6.

The gap at the side of the base end of the projection lens unit 6, whichincreases as the protruded length of the projection lens unit 6 from thefront end of the outer case 2 decreases, is filled with the extension 72of the power unit 7. The interior of the outer case 2 is thereforeeffectively used to miniaturize the projection display apparatus 1.

The power unit 7 contains various electronic parts in an L-shapedmetallic shield case 70. The shield case 70 acts as a ventilating pathfor circulating cooling air in the power unit 7. Also, the shield case70 prevents leakage of electrical and magnetic noises generated in thepower unit 7, and shields AC input and output lines accompanied with thepower unit 7 to shut out noises generated from them.

The shield case 70 stores a primary active filter, a power supply, and aballast or similar device not shown in the drawings. These devices mayinclude circuit boards including various electronic components. Forexample, the circuit board of the primary active filter includescomponents such as a transmission FET. The circuit board of the powersupply includes a rectifier diode bridge, an oscillating transistor fora D/D converter and a triode regulator for a D/D converter. The circuitboard of the ballast includes a driving FET for a chopper circuit and areverse-current preventing diode for a chopper circuit. Because thesedevices are heat sources, they are fixed to heat sinks to enhancecooling efficiency.

Various optical parts are densely packed in the outer case 2 so as notto form a dead space. It is therefore difficult to provide aconventional metallic chassis over the entire outer case 2. A flexibleshielding sheet (not shown) can cover the entire case without forming adead space.

The optical system assembled in the optical unit 10 is described withreference to FIG. 4. The optical system in accordance with thisembodiment includes an illuminating optical system 923 that includes alight source lamp unit 8, integrator lenses 921 and 922 and a polarizedlight conversion device 920. The optical system includes acolor-separating optical system 924 for separating the light beams Wemerging from the illuminating optical system 923 into red (R), green(G) and blue (B) light beams. Three liquid crystal light valves 925R,925G and 925B modulate the color light beams. A prism unit 910recombines the modulated light beams and a projection lens unit 6expansively projects the recombined light beams on a screen.

The light source lamp 81 of the light source lamp unit 8 is providedwith a lamp 805 such as a halogen lamp, a reflector 806 and a glass face807 adhered to the front surface of the reflector 806. The light sourcelamp 81 is stored in a housing 802 so as to expose the glass face 807(see FIGS. 3 and 8). The light from the lamp 805 emerges toward theintegrator lens 921 of the optical lens unit 9 through the glass face807 in the direction perpendicular to the direction of the apparatus 1.

The light source lamp 81 may be a halogen lamp, a metal halide lamp, axenon lamp or the like.

The illuminating optical system 923 includes two integrator lenses 921and 922, each of which includes a matrix of fine lenses. A polarizedlight conversion device 920 is disposed parallel to the integratorlenses 921 and 922 and a collective lens 930 is disposed perpendicularto the polarized light conversion device 920. A reflection mirror 931 isprovided in front of the collective lens 930, i.e., between thepolarized light conversion device 920 and the collective lens 930. Thereflection mirror 931 perpendicularly reflects the central optical axisla from the light source lamp 81 toward the front section of theapparatus.

The integrator lens 921 divides the light beams from the light sourcelamp unit 8 into a plurality of partial light beams which are collectednear the integrator lens 922.

The integrator lens 922 arranges central optical paths of partial lightbeams from the integrator lens 921 so as to be parallel to the opticalaxis la. When light beams from the light source lamp unit 8 areperfectly parallel to the optical axis 1a, the central optical path ofeach partial light beam from the integrator lens 921 is also parallel tothe optical axis 1a. Therefore, the integrator lens 922 may be omittedwhen the light beams from the light source lamp unit 8 are highlyparallel to the optical axis 1a.

The collective lens 930 collects partial light beams onto the lightvalves 925R, 925G and 925B.

As described above, in the projection display apparatus 1 in accordancewith this embodiment, the light beams from the light source lamp unit 8are divided into a plurality of partial light beams with the integratorlens 921. The partial light beams are collected onto the liquid crystallight valves 925R, 925G and 925B by the collective lens 930. Therefore,the liquid crystal light valves 925R, 925G and 925B can be illuminatedwith substantially uniform light, resulting in an image having lessirregular illumination.

The polarized light conversion device 920 includes an integration of apolarized light separation film and a λ/2 phase plate in which theincident light is separated into P-polarized light and S-polarized lightand then unified into S-polarized light. As shown in FIG. 5, thepolarized light conversion device 920 is provided with a polarized beamsplitter array 9201 and a selective phase plate 9202. The polarized beamsplitter array 9201 includes a plurality of pillar transparent plates9203 each bonded to each other and having a cross-section in the form ofa parallelogram. Polarized light separation films 9204 and reflectionfilms 9205 are alternately disposed between the transparent plates. Thepolarized beam splitter array 9201 is made by bonding a plurality ofglass plates having these films so as to alternately arrange thepolarized light separation films 9204 and reflection films 9205. Theglass plates are obliquely cut at a given angle.

The unpolarized light from the integrator lenses 921 and 922 (shown inFIG. 4) is separated into S-polarized light and P-polarized light withthe polarized light separation film 9204. The S-polarized light issubstantially vertically reflected by the polarized light separationfilm 9204 and vertically reflected by the reflection film 9205. TheP-polarized light passes through the polarized light separation film9204. The selective phase plate 9202 comprises a λ/2 phase layer 9206formed on the surface of the transparent plate 9203 which transmits thelight passing through the polarized light separation film 9204. The λ/2phase layer is not formed on the surface of the transparent plate 9203which transmits the light reflected from the reflection film 9205. TheP-polarized light passing through the polarized light separation film9204 therefore emerges after being converted to S-polarized light by theλ/2 phase layer 9206. As a result, substantially S-polarized light beamsemerge from the polarized light conversion device 920.

The use of only the S-polarized light improves color separationcharacteristics of dichroic mirrors 941 and 942 (shown in FIG. 4) of thecolor separating optical system 924 described below in relation to useof unpolarized light. Further, the S-polarized light has a higherreflectance than that of the P-polarized light to the mirror, and thuslight loss by reflection can be suppressed.

Referring to FIG. 4, the color separating optical system 924 includes ablue and green light reflecting dichroic mirror 941, a green lightreflecting dichroic mirror 942 and a reflection mirror 943.

In the color separating optical system 924, light beams (W) are radiatedto the blue and green light reflecting dichroic mirror 941, and the redlight beam passing through the mirror 941 is perpendicularly reflectedby a rear reflection mirror 943 and emerges from a red light emergingsection 944 toward a prism unit 910.

Blue light beams (B) and green light beams (G) in the light beams (W)are perpendicularly reflected by the blue and green light reflectingdichroic mirror 941 toward the green light reflecting dichroic mirror942. Only green light beams are perpendicularly reflected by the greenlight reflecting dichroic mirror 942 and emerge from a green lightemerging section 945 toward the prism unit 910. The blue light beams (B)passing through the green light reflecting dichroic mirror 942 emergefrom a blue light emerging section 946 through a light-guiding system927 toward the prism unit 910.

The light-guiding system 927 leads the blue light beams (B) to thecorresponding liquid crystal light valve 925B and includes an incidentside reflection mirror 971, an emerging side reflection mirror 972, anintermediate lens 973 provided therebetween and a collective lens 976provided ahead of the incident side reflection mirror 971. The distanceto the blue (B) light emerging section 946 is the longest amongdistances from the illuminating optical system 923 to red (R), green (G)and blue (B) light emerging sections 944, 945 and 946. Provision of thelight-guiding system 927 prevents light loss.

Red (R) and blue (B) light emerging sections 944 and 945 of the colorseparating optical system 924 are provided with collective lenses 951and 952, respectively. Red light beams (R) and green light beams (G)emerging from their respective emerging sections 944 and 945 areparalleled by their respective collective lenses 951 and 952.

Parallel red light beams (R) and green light beams (G) are incident onliquid crystal light valves 925R and 925G through polarizing plates 981and 982 and are modulated into image information. A driving means (notshown) switches the light valves 925R and 925G in response to the imageinformation to modulate color light beams passing through.

As with the red and green light beams (R) and (G), the blue light beams(B) passing through the light-guiding system 927 are paralleled by thecollective lens 953 provided at the blue (B) light emerging section 946.The blue light beams are incident on the liquid crystal valve 925Bthrough a polarizing plate 983, and are modulated in response to theimage information.

The liquid crystal valves 925R, 925G and 925B may use a polysilicon TFTas a switching device.

The modulated color light beams from the liquid crystal panels 925R,925G and 925B are incident on the prism unit 910, which includes adichroic prism, and are recombined. The recombined color image isexpansively projected through the projection lens unit 6 onto aprojection screen provided at a given position.

In the optical unit 10 in accordance with this embodiment, theilluminating optical system 923, the color separating optical system924, the liquid crystal light valves 925R, 925G and 925B, the polarizingplates 981 to 983, and the light-guiding system 927 are arranged in theabove-mentioned light guides 901 and 902 (shown in FIG. 3) after theoptical axis is aligned.

In this embodiment, light beams emitted from the light source lamp unit8 are reflected by the reflection mirror 931, travel a long L-shapedoptical path and reach the prism unit 910 through the color separatingoptical system 924. The optical path is therefore preferred to be aslong as possible, since individual optical parts are arranged in thenarrow region. Thus, the light beams from the light source lamp unit 8are paralleled and transmitted to the liquid crystal valves 925R, 925G,and 925B while lenses having low F values are used and positioning spaceof the integrator lenses 921 and 922 and the polarized light conversiondevice 920 are sufficiently secured. Since a wide space is secured forthe integrator lenses 921 and 922, the number of division of the lensescan be increased. The integrator lenses 921 and 922, therefore, can bearranged close to each other, resulting in miniaturization of theapparatus.

The structure for cooling the projection display apparatus in accordancewith the embodiment is described with reference to FIGS. 3, 6 and 7. Inthe apparatus 1, fresh air (cooling air) drawn from a cooling air intakeport 150 formed in the outer case 2 is circulated in the outer case 2 tocool heat sources in the case 2. The air is exhausted from an air outlet160 on the rear end of the outer case 2.

The cooling air intake port 150 includes a plurality of vent holes 151formed on the bottom wall 4a of the lower case 4 shown in FIG. 3. Thesevent holes 151 are formed over the region 150A under the prism unit 910and the region 150B under the base end of the projection lens unit 6.

A spongy air filter 241 covers the entire regions 150A and 150B havingthe vent holes 151. An air filter cover 23 is fixed with screws to theexterior of the bottom wall 4a of the lower case 4 to enclose the spongyfilter 241. The air filter cover 23 also has a number of vent holes 231.The air filter is provided so as to cover both regions 150A of theoptical lens unit 9 and 150B of the projection lens unit 6. A singlecover structure saves labor for exchanging the air filter 241 andimproves dust control.

The second half of the cooling air intake port 150, i.e., the region150A under the prism unit 910, is provided with a suction fan 15 asshown in FIG. 7. The suction fan 15 is fixed to the lower face of thebottom wall 92 of the head plate 903 mounting the prism unit 910. Thebottom wall 92 of the head plate 903 is provided with a vent hole (notshown) for circulating the cooling air.

The first half of the cooling air intake port 150, i.e., the region 150Bunder the projection lens unit 6, is formed near the extension 72 of thepower unit 7 which is located on the base end of the projection lensunit 6. As shown FIG. 6, the end of the extension 72, i.e., the end ofthe shield case 70 at the side of the projection lens unit 6, is used asan inlet for a ventilating path formed in the case 70. The rear end ofthe main body 71 or the end of the shield case 70 is used as an outletof the ventilating path.

The inlet of the ventilating path is provided with an auxiliary coolingfan 17 which acts as a cooling air conducting means, i.e., a suction fanfor introducing cooling air into the power unit 7. The auxiliary coolingfan 17 introduces air into the ventilating path through the inlet at thefront section of the shield case 70. The air in the ventilating path isexhausted from the outlet at the rear section of the case 70.

The auxiliary cooling fan 17 and the region 150B under the projectionlens unit 6 are connected to each other by a duct cover 170. The ductcover 170 forms a duct section defining an air path as shown in FIG. 3to directly introduce fresh air from the cooling air intake port 150 tothe power unit 7.

An air outlet 160 with an exhaust fan 16 are provided at the rear end ofthe apparatus, i.e., behind the power unit 7 and the light source lampunit 8. The air outlet is provided at the rear end of the apparatus sothat air is not exhausted onto users. The exhaust fan 16 is attached tothe housing 802 so as to cover the opening formed on the side face ofthe housing 802 of the light source lamp unit 8 and exhausts the air inthe outer case 2 through the housing 802.

In the above-mentioned projection apparatus 1, the cooling air intakeport 150 may include a suction fan 15 provided under the prism unit 910.The prism unit 910 may be surrounded on three sides with liquid crystallight valves 925R, 925G and 925B at given distances. The front side ofthe prism unit 910 faces the projection lens unit 6. The control board13 covers the upper face of the optical unit 10 and has a cutout section130 at the position corresponding to the prism unit 910. A video board11 may be overlaid upon the control board 13.

Air introduced from the cooling air intake port 150 is drawn to theexhaust fan 16 and rises along the side faces of the prism unit 910 asshown by arrow A1 of FIG. 7 to cool the prism unit 910, the liquidcrystal valves 925R, 925G and 925B, and the polarizing plates 981-983.The cooling air that reaches the upper portion of the prism unit 910 isdrawn by the exhaust fan 16 toward the light source lamp unit 8 throughthe space between the video board 11 and the control board 13, as shownby arrow A2 in FIG. 7. The air cools the light lamp unit 8 and isexhausted from the air outlet 160. The circuits on the boards 11 and 13can therefore be cooled by the cooling air introduced from the bottomwall of the outer case 2 to the air path. Because the cooling air coolsthe hot light source lamp unit 8 after cooling the boards 11 and 13, ahigh cooling efficiency can be achieved.

The cooling air from the cooling air intake port 150 provided at thebottom wall of the outer case 2 cools at least the prism unit 910, theliquid crystal light valves 925R, 925G and 925B, the polarizing plates981-983 and the light source lamp unit 8. Because these parts aredensely arranged in the narrow region, they can be effectively cooled,resulting in improved reliability of the optical elements.

The cooling air (fresh air) is also drawn from the cooling air intakeport 150 by means of the auxiliary cooling fan 17 provided on the powerunit 7. The air is introduced into the power unit 7 through the ductcover 170, i.e., the ventilating path in the shield case 70 as shown byarrow A3 of FIG. 6. The cooling air is drawn by the exhaust fan 16through the interior of the power unit 7 from the extension 72 to themain body 71 in order to cool the power unit 7, and is exhausted fromthe air outlet 160.

The heat sinks provided on the electronic components in the power unit 7must also be cooled. Because the cooling air (fresh air) from thecooling air intake port 150 is directly introduced to the ventilatingpath in the shield case 70, the heat sinks can be effectively andsecurely cooled. Direct supply of the low-temperature fresh cooling airto the power unit 7 efficiently dissipates heat from the heat sinks ascompared with the introduction of air that has already cooled otherparts.

Because the auxiliary cooling fan 17 and the first half of the coolingair intake port 150 are connected to each other through the duct cover170, only fresh air can be introduced from the exterior of the outercase 2 to the ventilating path in the shield case 70. Thus, the powerunit 7 is efficiently cooled.

The use of the auxiliary cooling fan 17 enables a stable supply of alarge volume of fresh air to the ventilating path, ensuring efficientcooling of the power unit 7.

Further, the auxiliary cooling fan 17 is connected to the cooling airintake port 150 through the duct cover 170. Such a configurationsecurely prevents dust from being sucked through the space between theprojection lens unit 6 and the outer case 2 when the fan 17 is operated.Dust is prevented from adhering onto the optical system and a highquality display image is obtained with high reliability.

As shown in FIGS. 3 and 6, temperature-sensing elements S1 and S2 aredirectly mounted on the control board 13 near heating sources, i.e., theprism unit 910, the liquid crystal light valves 925R, 925G and 925B, andthe light source lamp unit 8. The temperature sensing elements S1 and S2monitor extraordinary temperature fluctuations of the air heated by theheat sources. Direct mount of the temperature-sensing elements S1 and S2on the control board 13 eliminates the need for additional wiring.

In the optical unit 10 in this embodiment as shown in FIG. 8,ventilating paths that include vertical gaps are provided between thetwo integrator lenses 921 and 922 and between the integrator lens 922and the polarized light conversion device 920. A plurality of intakeports 909 are provided at regions below the integrated lenses 921 and922 and the polarized light conversion device 920. These gaps and intakeports 909 form optical paths which also circulate cooling air along atleast one face of the light incident face and the light emerging face ofeach of the integrator lenses 921 and 922 and the polarized lightconversion device 920.

A guide plate 89 is provided above the integrator lenses 921 and 922 andthe polarized light conversion device 920 to introduce cooling air. Thecooling air is circulated along at least one face of the light incidentface and the light emerging face of each optical element to a hood 848which is provided on a housing 802 of the light source lamp unit 8.

The integrator lenses 921 and 922 and the polarized light conversiondevice 920 are cooled with the cooling air drawn from the cooling airintake port 150 by the suction fan 15.

The cooling air introduced from the cooling air intake port 150 into theouter case 2 is drawn by the exhaust fan 16 provided behind the lightsource lamp unit 8 and introduced into the optical lens unit 9 throughthe intake ports 909 of the lower light guide 902. The cooling air risesin the ventilating paths along the light incident face and emerging faceof the integrator lenses 921 and 922 and the polarized light conversiondevice 920 as shown by arrows A7 of FIG. 8.

Because the polarized light conversion device 920 partially absorbsincident S-polarized light through the polarized light separation film9204 and the reflection film 9205 (see FIG. 5), it becomes heated.Accordingly, ventilating paths are provided along the polarized lightconversion device 920 to securely cool it with circulating cooling air.

The cooling air which rises between the polarized light conversiondevice 920 and the integrator lenses 921 and 922 is introduced to thehood 848 of the housing 802 along the guide plate 89, as shown by arrowA8 of FIG. 8. The air that has risen then enters into the housing 802 tocool the light source lamp 81 and is exhausted via the air outlet 160.

Because the cooling air which cools the polarized light conversiondevice 920 and the integrator lenses 921 and 922 is conducted to thelight source lamp unit 8 by the guide plate 89, it can securely andeffectively cool the light source lamp unit 8.

A portion of the cooling air that is introduced into the optical lensunit 9 is drawn toward the light source lamp unit 8 by the exhaust fan16 and rises along the glass face 807 of the light source lamp unit 81to cool the glass face 807, as shown by arrow A9 of FIG. 8. The airwhich cools the glass face 807 is drawn into the housing 802 through thehood 848 of the housing 802 and is also drawn into the gaps between thelight source lamp 81 and the housing 802 to cool the light source lamp81. The air is then exhausted through the air outlet 160.

Accordingly, the light source lamp 81 and the optical elements areefficiently maintained at a cool temperature, resulting in morereliability for the lamp 81 and the optical elements and requiring lessfrequent changing of the light source lamp 81.

Although the above-mentioned embodiment describes an apparatus in whichthe inlet of the ventilating path of the power unit 7 is formed on theend face of the shield case 70 at the side of the projection lens unit6, the inlet may be provided on many alternative surfaces, for example,on the front side face of the shield case at the projection face. Inthis case, the cooling air intake port may be provided on the side faceof the outer case 2 at the projection face side to directly connect thecooling air intake port with the inlet of the ventilating path.

The power unit 7 is cooled with great efficiency because a cooling airconducting means is provided for directly introducing fresh air into aventilating path provided inside the power unit. Direct introduction offresh air into the ventilating path permits cooling of the interior ofthe power unit by fresh air, which is cooler than the air in the outercase 2, and accordingly results in greater cooling efficiency.

Also, a ventilating path is provided to direct the cooling air along thepolarized light conversion device in the outer case 2. The ventilatingpath securely circulates the cooling air near the polarized lightconversion device regardless of the structure of the projection displayapparatus, resulting in a satisfactory cooling effect.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations may be apparent to those skilled in the art. Accordingly,the preferred embodiments of the invention as set forth herein areintended to be illustrative, not limiting. Various changes may be madewithout departing from the spirit and scope of the invention as definedin the following claims.

What is claimed is:
 1. A projection display apparatus comprising:anoptical unit that includes a light source and a projection lens, theoptical unit forming an optical image in response to image informationby optically treating light beams emitted from the light source lamp,and expansively projecting the optical image through the projectionlens; a circuit board provided on said optical unit, said circuit boardcomprising a temperature-sensing element adjacent to said light sourcelamp; a power unit; an outer case that stores the optical unit and thepower unit and includes a ventilating fan that ventilates the interiorof the outer case; a polarized light conversion device facing anemitting surface of the light source lamp that includes a light incidentface and a light emitting face, the polarized light conversion deviceseparating the light beams emitted from said light source lamp unit intotwo types of straight polarized light components and aligning apolarizing direction of the straight polarized light components; and aventilating path provided inside the outer case that circulates coolingair along at least one face among the light incident face and lightemitting face of the polarized light conversion device.
 2. Theprojection display apparatus according to claim 1, the ventilating fanbeing located adjacent to the light source lamp.
 3. The projectiondisplay apparatus according to claim 1, further comprising:a guide thatintroduces the cooling air circulated along at least one face among thelight incident face and light emitting face of the polarized lightconversion device to the light source lamp.
 4. The projection displayapparatus according to claim 1, the outer case comprising:an operatingsection having a plurality of switches including a main power on/offswitch, and a protruded section protruding from the main switch providedbetween the main switch and other switches adjacent to the main switch.5. The projection display apparatus according to claim 4, the protrudedsection being provided along a periphery of the main switch.
 6. Aprojection display apparatus comprising:an optical unit that includes alight source lamp and a projection lens, the optical unit forming anoptical image in response to image information by optically treatinglight beams emitted from the light source lamp and expansivelyprojecting the optical image through the projection lens; a power unit;an outer case that stores the optical unit and the power unit; apolarized light conversion device facing an emitting surface of thelight source lamp that includes a light incident face and a lightemitting face, the polarized light conversion device separating thelight beams emitted from the light source lamp into two types ofstraight polarized light components and aligning a polarizing directionof the straight polarized light components; a first ventilating pathprovided inside the outer case that circulates cooling air along atleast one face among the light incident face and the light emitting faceof the polarized light conversion device; a second ventilating pathprovided inside the power unit that circulates cooling air; a firstcooling air intake port that provides cooling air from outside of theouter case to the first ventilating path; and a second cooling airintake port that directly conducts cooling air from the outside of theouter case to the second ventilating path.
 7. The projection displayapparatus according to claim 6, further comprising a circuit boardprovided on said optical unit,said circuit board being provided with atemperature-sensing element adjacent said light source lamp.
 8. Theprojection display apparatus according to claim 6, the outer casecomprising a ventilating fan located adjacent to the light source lamp.9. The projection display apparatus according to claim 6, furthercomprising:a guide that introduces the cooling air circulated along atleast one face among the light incident face and light emitting face ofthe polarized light conversion device to the light source lamp.
 10. Theprojection display apparatus according to claim 6, said outer casecomprising:an operating section having a plurality of switches includinga main power on/off switch, and a protruded section protruding from themain switch provided between the main switch and other switches adjacentto the main switch.
 11. The projection display apparatus according toclaim 10, the protruded section being provided along a periphery of themain switch.